1. Field of the Invention
This invention relates to an apparatus for detecting movement of a television image in response to frame difference data representing the difference between present frame date and previous frame data and, more particularly, is directed to a television image movement detecting apparatus applicable, for example, to a video signal standard conversion circuit.
2. Description of the Prior Art
A block matching method has been used to detect movement vectors each representing the amount and direction of movement of a television image from one frame to the next in response to frame difference data between present frame data and previous frame data. In such block matching method, a video signal is divided into a number of segmental areas or blocks for each frame. The frame difference data are produced for each of the segmental areas by calculating differences in the positions or coordinates of picture elements representing corresponding segmental areas of successive frames. These calculations are effected by a digital computer operable in accordance with a program stored in the computer memory.
In order to simplify the program arrangement and increase the signal processing speed, it has been proposed to designate a point or pixel representative of each of the segmental areas. The representative pixel is normally set at the center of the segmental area. In such case, the frame difference data are produced by calculating differences in the position or coordinates of the pixel representative of a segmental area of one frame relative to the position or coordinates of the respective picture element of the corresponding segmental area of the subsequent frame.
One disadvantage of such representative pixel method is that it fails to detect small movements of an object of uniform brightness. This is particularly true when the moving object appears against a distinctive background which changes greatly across the image.